Heat oil in a very large high-sided skillet or wok over high heat. Add the mushrooms; cook, stirring, for about 1 min.
Add the onion and garlic. Cook, stirring constantly, until slightly softened, about 5 min. Add the pork and broccoli; cook, stirring constantly, until the pork begins to brown, about 5 min.
Add the water chestnuts, broth and sesame oil; cook for 2 min. Garnish with sesame seeds. Serve on its own or with rice, rice noodles or quinoa.
To make ahead, slice the pork tenderloin into medallions and then into thin strips; place in freezer bag and freeze for up to a month.